Earlier this year an app came out for the iPhone and within weeks it had a line of a million users waiting to get access to it. It wasn't an app that let you spin a globe or another that let you play a range of instruments. It was a basic e-mail app called Mailbox.

Mailbox, which was bought by Dropbox for around $100 million in March, has a different take on dealing with e-mail overload, and today it's being released for the iPad.

"Whether you like it or hate it, you have to use email. You don't get a choice. It's the world's collaboration system," Mailbox CEO Gentry Underwood told ABC News. "We target those people who feel crushed by it. We built an experience that is more delightful. That's where we found our sweet spot."

The iPad app has all the core features of the iPhone app. You can do four things with each message by simply swiping the message to the right or left: delete it, archive it, set a reminder about it or add it to a to-do list. The iPad app has some small differences, though. The menu on the left side can be kept open and it has also been adjusted to support external Bluetooth keyboards. The apps look a lot like Apple's native e-mail app, making it very easy for most to adjust to it. It doesn't, however, work in portrait mode yet.

When we reviewed the app, we found it tackled email issues a new way, but noted that it took a lot of time to go through each message. We also knocked it because it was only available for the iPhone and Gmail users.

However, Underwood says that users are sticking with the app at an extremely high rate and that the number one priority now is working to get other email services working with the app and to bring it to Android and more phones. There's interest in making a desktop or web-based client.

"When we talk about living in a mobile era it doesn't mean we just use phones," he said. "We live in a multi-screen world. From a high level it is a no-brainer that we should have a desktop experience that is consistent and complimentary to the mobile."

For those who don't have access to Mailbox now, there are a slew of other email apps and add-ons that look to improve your email productivity, including SaneBox and Unroll.me. Check out our guide to those email services here.